1. Technical Field
The present invention relates to a method of surface modifying a polyimide film, a method of manufacturing a flexible copper clad laminate (FCCL) using the same, and a FCCL having a two-layer structure manufactured thereby. More particularly, the present invention relates to a method of surface modifying a polyimide film, comprising modifying the surface of a polyimide film through first plasma treatment, dipping the polyimide film into a solution containing an ethyleneimine-based silane coupling agent, and then modifying the surface of the polyimide film through second plasma treatment, a polyimide FCCL having a two-layer structure using the method of modifying the surface of a polyimide film, and to a polyimide FCCL having excellent adhesive strength manufactured using the manufacturing method.
2. Description of the Prior Art
A polyimide film has heat resistance, electrical properties, chemical resistance, and bending resistance that are superior to other polymer materials, and thus may be variously used as insulating substrate material for electronic parts, such as a flexible printed circuit board (FPCB), tape automated bonding (TAB), COF (Chip On Film), etc. A conventional FCCL (Flexible Copper Clad Laminate) used in an FPCB is exemplified by a FCCL having a three-layer structure using an epoxy adhesive. However, such a FCCL has deteriorated dimensional stability because the heat resistance of the adhesive is poor. Hence, the conventional FCCL has been deemed unsuitable for fine patterning.
Recently, thorough attempts have been made to replace a conventional product having a three-layer structure with a product having a two-layer structure. The product having a two-layer structure is realized by directly die-casting a polyimide film to a copper foil or bonding a polyimide film to a copper foil at a high temperature without the need for an adhesive layer, and therefore, provides advantages such as easy formation of fine patterns and high flexibility. Moreover, by virtue of the above-mentioned advantages, a FCCL having a two-layer structure may be more widely marketable for use in display products, such as folding mobile phones, LCDs, PDP modules, etc.
In particular, since Korea mainly imports substrate materials for use in electronic parts, the development of a two-layered FCCL using a novel process has been urgently required.
A method of manufacturing a two-layered FCCL by laminating a polyimide film and a copper foil, rather than using an adhesive, has been reported.
In addition, sputtering-electroplating methods have been proposed, in which a thin metal seed layer (nickel, chromium, etc.) is formed through sputtering, and then a copper layer is formed to a desired thickness through electroplating thereon. However, the above method suffers because the surface modification of the polyimide film should be preceded using plasma or ion beams, during which a specific seed layer is needed. Particularly, when a double-sided FCCL is manufactured, specific equipment is needed, thus the manufacturing coat becomes increased. Further, since the adhesive strength of the FCCL becomes poor under conditions of high temperature and high humidity, reliability is decreased. Furthermore, a drilling process, which is conducted after a printed circuit board is manufactured, may cause environmental contamination.
Leading to the present invention, intensive and thorough effort to obtain two-layered FCCLs, carried out by the present inventors, aiming to avoid the problems encountered in the related art, led to the development of a method of manufacturing a FCCL having a two-layer structure, comprising modifying the surface of a polyimide film through first plasma treatment, dipping into a solution containing a predetermined ethyleneimine-based silane coupling agent for surface treatment and then second plasma treatment, and sequentially copper sputtering and electroplating the surface modified polyimide film under optimal conditions, thus the single-sided or double-sided FCCL can be used for fine wiring process by directly laminating copper to the polyimide film, and can maintain good adhesive strength between the film and the copper foil even at high temperatures for a long period of time.